Some wireless service providers allow for both “interconnect” and “dispatch” calls to be placed over a wireless network. Interconnect capability is traditionally referred to as cellular communications offering full duplex voice transmission via the use of dial-up calling. The dispatch capability is often referred to as a “walkie-talkie” communication using half duplex voice transmission where only one party is capable of talking at any one time. Sprint Nextel Inc. is a leading provider of such dual capability service, having subscriber units adapted for making both interconnect voice and dispatch voice calls. In a network such as Sprint Nextel's, the walkie-talkie feature is operated by a user selecting a number within an established “fleet” of subscribers, and having the user press a dispatch button to initiate the communication. The mobile station/subscriber unit radio sends a signal including subscriber identification information, as well as the intended target number, to a cell site base station. A mobile station can be any type of wireless communication device including wireless telephones, wireless Personal Digital Assistants (PDA), wireless pagers, or any device which performs one or more of these functions. Subsequently, a signal is sent to a dispatch application processor (DAP) through a frame relay switch called a Metro Packet Switch. The DAP identifies the target radio and signal with a distinctive tone to join the call.
On the other hand, an interconnect voice call is initiated when a user dials a telephone number and presses the “send” key on the subscriber unit. The telephone number, along with other data signals, passes over a radio channel to the base station which, in turn, relays the signals and the telephone number to main switching equipment. From the switching equipment, a message is passed to the Public Switched Telephone Network (PSTN) to connect with the target telephone number. When the called number answers, a “traffic channel” is assigned to the call.
The capabilities of the dispatch portion of the system includes the sending of computer-type packet data as well as the above discussed dispatch data. A Mobile Data gateway (MDG) provides access to the Internet during packet data operation.